二酸化炭素分圧測定ブイを用いた南極海域の観測脇田昌英

(1)

二酸化炭素分圧測定ブイを用いた南極海域の観測

脇田昌英¹、中野善之¹、飯田高大²、渡邉修一¹

1海洋研究開発機構

2国立極地研究所

Observation in the Antarctic Sea using pCO

2

autonomous buoy

Masahide Wakita

¹

, Yoshiyuki Nakano

¹

, Takahiro Iida

²

and Shuichi Watanabe

¹

1

JAMSTEC

2

NIPR

The total ocean uptake flux including the anthropogenic CO

2

was estimated to be 2.0  1.0 Pg-C/yr in a reference year 2000 by Takahashi et al.(2009). The contribution of the seasonal ice-free zone of the Southern Ocean is estimated 0.06 Pg-C/yr.

This estimate is large diffrence from the previous study (Takahashi et al., 2002). The flux of CO

2

between air and sea is estimated using the difference of pCO

2

between air and sea surface and the gas transfer coefficient. That difference is due to the luck of data in the southern ocean. A sampling strategy of pCO

2

measurement to estimate the annual mean CO

2

uptake by the southern ocean to 0.1PgC/yr was discussed by Lenton, Matear and Tilbrook (2006) . They suggested that sampling regularly every 3 months, at every 30 degree in longitude and 3 degree in latitude is sufficient to determine the net Southern Ocean CO

2

uptake which uncertainty has less than 0.1PgC/yr.

We have been developed the small drifting buoy system (diameter 250-340 mm, length 470 mm, weight 15 kg) for CO

2

autonomous measurement by using spectrophotometry with the support of the Japan EOS Promotion Program (JEPP), the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and tested at the Kerguelen Plateau area in the eastern Indian sector of the Southern Ocean in January 2009. Preliminary results obtained with two autonomous pCO

2

buoys are comparative with other data. The observed pCO

2

values are around 200 atm near the south-east of Kerguelen Plateau from Janually to March and 280-350 atm off the Plateau between April and August.

About 10 autonomous pCO

2

buoys would be distributed in the seasonal ice-free zone of the Southern Ocean accouding the Lenton’s sampling strategy in 2012-2013. We will try to determine the ocean uptake flux with small uncertainty.

Reference: Takahashi et al.(2009) Deep-Sea Res. II, 56, 554–577 Takahashi et al.(2002) Deep-Sea Res. II, 49, 1601–1622.

Lenton, Matear and Tilbrook (2006) Global Biogeochem. Cyckes, 20, GB4010, doi:10.1029/2005GB002620.

Takahashi

ら

(2009)

は人為起源二酸化炭素を含んだ海洋の二酸化炭素の吸収を

2000

年基準で

2.0  1.0Pg-C/yr

と見

積もっている。南大洋の季節海氷域の寄与は

0.06 Pg-C/yr

とかなり小さく見積もっている。

Takahashi

ら

(2002)

で見積もった値とかなり異なっている。大気海洋間のフラックスは、大気・海洋間の二酸化炭素分圧の差と気体交換係数によって求められる。先の主な原因は南大洋のデータが不足していることによっている。

Lenton, Matear,

Tilbrook (2006)

は

3

カ月間隔に経度方向に

30

度、緯度方向に

3

度での観測が実施出来れば、

0.1Pg-C/yr

の精度で

見積もれるとモデルを用いて示している。

文部科学省の

JEPP

の支援を受けて、小型の二酸化炭素測定用漂流ブイシステムを開発し、

2009

年

1

月にケルゲレン海台付近で投入、観測試験を行った。小型二酸化炭素測定用漂流ブイシステムから得られたデータはこれまでのデータを矛盾しなかった。観測された二酸化炭素分圧は、

1-3

月のケルゲレン海台南東部で

200 atm

、

4-8

月のケルゲレン海台の外側で

280-350 atm

であった。

約

10

台の小型二酸化炭素測定用漂流ブイシステムを

2012

－

2013

年に南大洋の季節海氷域に

Lenton

ら

(2006)

が示した観測時空間スケールでの観測を予定している。この結果を用いてより精度の高い二酸化炭素吸収量を求めることを試みる。

参考文献

二酸化炭素分圧測定ブイを用いた南極海域の観測 脇田 昌英

Observation in the Antarctic Sea using pCO

autonomous buoy

Masahide Wakita

, Yoshiyuki Nakano

, Takahiro Iida

and Shuichi Watanabe

JAMSTEC

NIPR

The total ocean uptake flux including the anthropogenic CO

was estimated to be 2.0  1.0 Pg-C/yr in a reference year 2000 by Takahashi et al.(2009). The contribution of the seasonal ice-free zone of the Southern Ocean is estimated 0.06 Pg-C/yr.

This estimate is large diffrence from the previous study (Takahashi et al., 2002). The flux of CO

between air and sea is estimated using the difference of pCO

between air and sea surface and the gas transfer coefficient. That difference is due to the luck of data in the southern ocean. A sampling strategy of pCO

measurement to estimate the annual mean CO

uptake by the southern ocean to 0.1PgC/yr was discussed by Lenton, Matear and Tilbrook (2006) . They suggested that sampling regularly every 3 months, at every 30 degree in longitude and 3 degree in latitude is sufficient to determine the net Southern Ocean CO

uptake which uncertainty has less than 0.1PgC/yr.

We have been developed the small drifting buoy system (diameter 250-340 mm, length 470 mm, weight 15 kg) for CO

buoys are comparative with other data. The observed pCO

values are around 200 atm near the south-east of Kerguelen Plateau from Janually to March and 280-350 atm off the Plateau between April and August.

About 10 autonomous pCO

buoys would be distributed in the seasonal ice-free zone of the Southern Ocean accouding the Lenton’s sampling strategy in 2012-2013. We will try to determine the ocean uptake flux with small uncertainty.

Reference: Takahashi et al.(2009) Deep-Sea Res. II, 56, 554–577 Takahashi et al.(2002) Deep-Sea Res. II, 49, 1601–1622.

Lenton, Matear and Tilbrook (2006) Global Biogeochem. Cyckes, 20, GB4010, doi:10.1029/2005GB002620.

Takahashi

(2009)

2000

2.0  1.0Pg-C/yr

0.06 Pg-C/yr

Takahashi

(2002)

Lenton, Matear,

Tilbrook (2006)

3

30

3

0.1Pg-C/yr

JEPP

2009

1

1-3

200 atm

4-8

280-350 atm

10

2012

2013

Lenton

(2006)

: Takahashi et al.(2009) Deep-Sea Res. II, 56, 554–577 Takahashi et al.(2002) Deep-Sea Res. II, 49, 1601–1622.

Lenton, Matear and Tilbrook (2006) Global Biogeochem. Cyckes, 20, GB4010, doi:10.1029/2005GB002620.

二酸化炭素分圧測定ブイを用いた南極海域の観測脇田昌英